The present invention relates to a cold emission electrode, particularly, a cold emission electrode suitable for a discharge device using a cold emission phenomenon, a method of manufacturing the cold emission electrode, and a display device comprising the same.
A thermoelectronic emission phenomenon, photoemission phenomenon, cold emission phenomenon, and the like are known as electron emission phenomena in which electrons existing in an object are emitted into space. In practice, an electron emitting electrode material is used to form an electrode for a device utilizing discharge, such as a discharge lamp. For example, there is known a thermoelectronic emission discharge lamp using the thermoelectronic emission phenomenon in which electrons are emitted by supplying a current to, e.g., a coil filament to heat it.
Unlike the above example, devices using various types of discharge using electrodes utilizing cold emission phenomenon are also known. Field emission display devices using electron emission using a strong electric field, cold emission discharge tubes and plasma display panels utilizing secondary electron emission upon mainly ionic collision, and the like are commercially available.
Secondary electron emission as an electron emission mechanism unique to a cold emission discharge tube is potential type emission or kinetic type emission. In the potential type emission, electrons are emitted by an energy given by a so-called Auger effect, in which when a cation comes close to a cold cathode, the level of an electron lowers to the ground state of the cation because the level of the electron in the electrode is higher than that of the cation, and the energy generated by this level difference is applied to another electron. The kinetic type emission is emission from the cold cathode upon reception of an energy, the energy being generated when a cation comes into collision with the cold cathode. Glow discharge unique to the cold emission tube occurs due to the above electron emission mechanism.
A cold emission discharge fluorescent tube or plasma display panel which emits visible light upon this glow discharge comprises a vessel having a plurality of electrodes and an inner wall coated with a fluorescent material and a mixture of a rare gas and mercury sealed in the vessel. Electrons emitted in accordance with the photoemission phenomenon by light incident on the cold emission discharge fluorescent tube initially move by an electric field applied to the electrodes and come into collision with the gas and the like sealed in the vessel, thereby ionizing gas to produce ions. These ions collide with the electrodes to generate secondary electrons. The electrons emitted by the cold emission electrode collide with vaporous mercury atoms to start glow discharge, thereby generating ultraviolet rays. The fluorescent material is excited with the ultraviolet rays to emit visible light.
As the material of the cold emission electrodes, a metal element having a relatively low work function, such as nickel (Ni) or molybdenum (Mo) is used.
A cold emission discharge fluorescent tube having a cold emission electrode made of such a material has a higher luminance (cd/m.sup.2) with a decrease in its tube diameter. A low-profile device having the cold emission discharge fluorescent tube can be obtained and is suitable for the backlight of a liquid crystal display device.
A cold emission discharge fluorescent tube having a cold emission electrode has a high lamp discharge voltage and hence high lamp power consumption. In particular, it is difficult to perform display operation for a long period of time when the tube is used as a backlight in a battery-driven portable display device.
An electron emitting material is sputtered from the above metal electrode by discharge, and then the sputtered electron emitting material contaminates the tube wall and shortens the emission service life.